Head tracking servo pattern

ABSTRACT

A servo pattern for controlling a head position has a first pattern in which two frequency signals having respectively different frequencies are arranged alternately in the width direction of a track in a two-track cycle, and a second pattern which is repeated in a cycle of n tracks. The first and the second patterns are arranged in the longitudinal direction of the tracks so as to create a servo pattern with a wide servo capture range and so as also to ensure accurate detection.

This application is a continuation application of Ser. No. 08/456,043,filed May 31, 1995, now abandoned, which is a division of Ser. No.08/059,345 filed May 11, 1993, now U.S. Pat. No. 5,453,887, which was acontinuation application of Ser. No. 07/707,921 filed on May 28, 1991,now abandoned, which was a continuation application of Ser. No.07/143,518, filed on Dec. 31, 1987, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a head tracking servo pattern formed ona recording medium for controlling the position of a head, such as arecording/reproducing head or a reproducing head, and more particularlyto a recording medium having a tracking servo pattern and to a systemand a method for controlling the position of a reproducing head by usingsaid recording medium.

2. Description of the Prior Art

A first example of a prior art arrangement of a servo pattern is shownin FIG. 1. In FIG. 1, the servo pattern uses two signals havingfrequencies different from each other (referred to as a two-frequencytype servo pattern hereinafter). In this arrangement, servo patterns 2and 3 are recorded at positions shifted by a half-track pitch beforeeach data sector 1. These servo patterns 2 and 3 are burst signalshaving different frequencies f1 and f2, and are reproducedsimultaneously by a head running along the track. The reproduced signalsare separated into an f1 component and an f2 component by a frequencydiscriminator (not shown). The reproducing head positioning mechanism iscontrolled so that the ratio between the two components is substantiallyequal to 1.

A second prior art arrangement of a servo pattern has staggered bursttype servo patterns as shown in FIG. 2. In FIG. 2, A and B denote pulsetrains having different bit patterns. C, D, E and F are burst signalshaving the same frequency. The pulse interval is measured for the pulsetrains A and B, so that these pulse trains can be discriminated ordistinguished by measuring the number of the respective pulse intervalsthus measured. After at least one of the pulse trains A and B has beendetected, in order to perform servo control, a timing signal isgenerated for sampling the burst signals C, D, E and F, and theamplitudes of the reproduced signals of the burst signals C, D, E and Fare measured. Then, the head positioning mechanism is controlled by themeasured amplitude ratio of each reproduced signal.

In the first prior art arrangement of the servo pattern shown in FIG. 1,however, there is the problem that the same servo pattern is repeatedevery two tracks, so that the servo capture range is comparativelynarrow (for example, ±1 track).

Further, in the second prior art arrangement of the servo pattern shownin FIG. 2, the same servo pattern is repeated every four tracks, so thatthe servo capture range is wider at ±2 tracks. However, whendiscriminating the pulse trains A and B from each other, it is necessaryto accurately discriminate pulse intervals which are relatively close toeach other, and accordingly it is difficult to ensure accurate servooperations when noise is present.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a headtracking servo pattern which ensures exact control of the head position.

It is another object of the present invention to provide a head trackingservo pattern which permits a wide servo capture range and at the sametime ensures accurate servo control so as to solve the problems of theprior art arrangements.

It is a further object of the present invention to provide a headtracking servo pattern which is so arranged that, at any track position,two servo burst amplitude signals are reproduced in an adjacent mannerto minimize factors which cause errors in the head position control.

It is still a further object of the present invention to provide a headtracking control method which permits a wide servo capture range and atthe same time ensures accurate servo control so as to solve the problemsof the prior art arrangements, and to provide a head tracking controlsystem employing the method.

In accordance with a first aspect of the present invention, there isprovided a tracking servo pattern arrangement formed on a recordingmedium to control the position of a head with respect to a track on therecording medium, and the tracking servo pattern arrangement comprises:

a first pattern composed of first pattern elements bearing at least twofrequency signals, each having a different frequency, and the firstpattern elements being arranged alternately in the width direction ofthe track; and

a second pattern composed of second pattern elements repeated at aninterval of n tracks (n: an integer larger than 2), the first patternand the second pattern being arranged in the longitudinal direction ofthe track.

Here, the first pattern may indicate the starting position of the servopattern for head tracking.

The first pattern elements may be so arranged that the first patternelements extend over two adjacent tracks.

Each of the second pattern elements may extend over two adjacent tracks,and the second pattern elements may have different positions in thelongitudinal direction of the track.

Further, the plurality of signal patterns may have positionssequentially different in the longitudinal direction of the track.

The length of the first pattern elements in the longitudinal directionmay be different from the length of the second pattern elements in thelongitudinal direction.

The first pattern elements may each be arranged within one track withoutextending over two adjacent tracks and the second pattern elements mayeach be arranged within one track without extending over two adjacenttracks.

In accordance with a second aspect of the present invention, there isprovided a tracking servo pattern arrangement formed on a recordingmedium to control the position of a head with respect to one of aplurality of tracks arranged concentrically on the recording medium, andthe tracking servo pattern arrangement comprises:

a first pattern composed of first pattern elements bearing a pluralityof frequency signals arranged alternately at a first predetermined trackpitch in the width direction of the track in which the plurality oftracks are arranged; and

a second pattern composed of second pattern elements having a pluralityof signal patterns arranged alternatively at a second predeterminedtrack pitch in the width direction, the positions of the signal patternsin the longitudinal direction of the track being displaced from eachother.

Here, each of the signal patterns may bear a frequency signal.

The first pattern elements and the second pattern elements may bedisplaced from each other by a half track pitch in the width direction.

The first pattern elements and the second pattern elements may bearranged in phase in the width direction.

The first pattern elements and the tracks may be arranged in phase.

The first pattern elements and the tracks may be displaced from eachother by a half track.

Further, the first pattern elements may be arranged at intervals of onetrack in the width direction, while the first pattern elements aredisplaced from each other in the longitudinal direction.

In accordance with a third aspect of the present invention, there isprovided a tracking servo pattern arrangement formed on a recordingmedium to detect displacement of a head with respect to a track on therecording medium, and the tracking servo pattern arrangement comprises:

first patterns bearing frequency signals, each having a differentfrequency, the first patterns being arranged at the same positions inthe longitudinal direction of the track and alternately in the widthdirection of the track; and

second patterns bearing a plurality of frequency signals, each havingthe same frequency, the second patterns being arranged at differentpositions in the longitudinal direction, and the first patterns and thesecond patterns being adjacent to each other in the longitudinaldirection.

In accordance with a fourth aspect of the present invention, there isprovided an apparatus for detecting a tracking servo pattern arrangementformed on a recording medium to detect displacement of a head withrespect to a track on the recording medium, and the apparatus comprises:

a first detection means for detecting a first pattern formed on therecording medium and bearing frequency signals, each having a differentfrequency, the frequency signals being arranged in the width directionof the track; and

a second detection means for detecting a second pattern formed on therecording medium and having a plurality of elements displaced atdifferent positions in the longitudinal direction and arranged in thewidth direction, the second detection means detecting the headdisplacement in accordance with an arrangement of each of said elementsof the detected second pattern in the longitudinal direction.

Here, the apparatus may further comprise a head position control meansfor controlling the position of the head in response to an output signalfrom the second detection means.

The operation of the second detection means may be enabled after thefirst detection means detects the first pattern.

The second detection means may detect the head displacement inaccordance with positions of the elements of the detected second patternin the longitudinal direction.

In accordance with a fifth aspect of the present invention, there isprovided a method of controlling the position of a head by using atracking servo pattern arrangement recorded at spaced positions andperiodically on a recording medium, and the method comprises the stepsof:

reproducing the tracking servo pattern arrangement recorded on therecording medium sequentially;

storing amplitude data of the reproduced tracking servo patternarrangement in N memory regions;

discriminating whether amplitude data are stored in the N memory regionsor not;

assigning a binary level to each of the N memory regions in accordancewith the result of the discrimination step to obtain a N-bit code;

comparing the N-bit code with a predetermined code to identify the tracknumber at which the head is positioned; and

controlling an actuator for actuating the head in accordance with theamplitude data stored in the memory regions and the identified tracknumber.

According to the present invention, two signals having differentfrequencies are simultaneously reproduced by a head travelling on atrack so that the first pattern is easily and reliably detected. As aresult, the starting edge of the servo pattern is detected. In addition,the arrangement of the second pattern has a wide latitude, so that theservo capture range can be enlarged.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of preferred embodiments thereof taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate examples of prior art arrangements of trackingservo patterns;

FIGS. 3, 4, 5 and 6 illustrate various embodiments of a tracking servopattern arrangements according to the present invention;

FIGS. 7A and 7B illustrate a tracking servo pattern corresponding to thepattern shown in FIG. 3 and various waveforms relating to this pattern,respectively;

FIG. 8 illustrates a tracking servo pattern in another embodiment of thepresent invention;

FIGS. 9A and 9B illustrate a further embodiment of a tracking servopattern according to the present invention and various waveformsrelating to this pattern to explain tracking control according to thepresent invention, respectively;

FIG. 10 is a block diagram showing an embodiment of a head positioncontrolling system according to the present invention;

FIG. 11 is a flowchart showing an embodiment of a control procedureexecuted by the CPU shown in FIG. 10;

FIG. 12 illustrates a further embodiment of a tracking servo pattern inaccordance with the present invention;

FIGS. 13A and 13B illustrate a further embodiment of a tracking servopattern according to the present invention and various waveformsrelating to this pattern to explain tracking control according to thepresent invention, respectively;

FIG. 14 is a flowchart showing an embodiment of a control procedureexecuted by the CPU shown in FIG. 10;

FIGS. 15 and 16 illustrate further embodiments of a tracking servopattern in accordance with the present invention;

FIGS. 17A and 17B illustrate a further embodiment of a tracking servopattern according to the present invention and various waveformsrelating to this pattern to explain tracking control according to thepresent invention, respectively;

FIG. 18 is a flowchart showing an embodiment of a control procedureexecuted by the CPU shown in FIG. 10; and

FIGS. 19, 20, 21 and 22 illustrate further embodiments of a trackingservo pattern according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows a first embodiment of the present invention. In FIG. 3,reference numeral 4 denotes a data sector. Reference numeral 5 denotes aburst signal having a frequency of f1,and reference numeral 6 denotes aburst signal having a frequency of f2. G, H, I and J designate burstsignals for servo control having the same frequency (hereinafterreferred to simply as servo burst signals).

The above-described arrangement will be discussed when a head, such as arecording/reproducing head or a reproducing head, travels along a track4n+2. After the head has read out the data from a sector N, burstsignals 5 and 6 are reproduced simultaneously, and the frequencycomponents f1 and f2 contained in the burst signals 5 and 6 arediscriminated or distinguished from one another by a discriminatingcircuit. The discriminating circuit is so arranged that if either of thesignal exists, amplitude sampling signals for sampling the servo burstsignals are generated.

The reason for using signals with different frequencies (f1 and f2) hereis to prevent unstable detection in the discriminating circuit. If thesame frequency were used, the signals might cancel each other due tophase shifts, so that the detection would be unstable. Furthermore, thefrequencies f1 and f2 are selected to be different from the datarecording frequency (generally, the frequencies f1 and f2 are lower than"the data recording frequency"), so there is no possibility of erroneousdetection in the data sector 4.

A total of four amplitude sampling signals are generated to sample theservo burst signals, in such a manner that each of the amplitudesampling signals corresponds to a respective one of the servo burstsignals G, H, I and J. The amplitudes of the servo burst signals G, H, Iand J are measured in synchronism with the amplitude sampling signalsfor sampling the servo burst signals. In this example, the servo burstsignals G and H are not detected, and the servo burst signals I and Jare detected. Here, the head position is controlled so that theamplitudes of the servo burst signals I and J are equal to each other.For example, if we suppose that an off track displacement of +1 trackhas occurred, that is, the head is positioned on the track 4n+3, thenthe servo burst signals G and J would be detected as having the sameamplitude, so that it can be judged that there is an off trackdisplacement of +1 track.

Next, if we suppose that an off track displacement of +2 tracks hasoccurred (when the head is positioned on the track 4n+4), the servoburst signals G and H would be detected as having the same amplitude.However, since this would also happen if an off track displacement of -2tracks had occurred (that is, if the head were positioned on the track4n), it would not be possible to judge the direction of the off trackdisplacement. Consequently, the servo capture range for the arrangementshown in FIG. 3 is ±2 tracks, which is the same as in the prior artarrangement shown in FIG. 2, but the FIG. 3 arrangement has theadvantage that the starting edge of the servo signal can be detected bydetecting the servo pattern having the two frequencies f1 and f2.

FIG. 4 shows a second embodiment of the present invention. In FIG. 4,reference numeral 7 denotes a data sector. Reference numeral 8 denotes aburst signal which has a frequency of f1 and which lasts for a period oftime longer than the duration of the burst signal 5 shown in FIG. 3.Reference numeral 9 denotes a burst signal which has a frequency of f2and which lasts for the same period of time as the burst signal 8. Thesame servo system as that used with the prior art arrangement shown inFIG. 1 can be used here, or the same servo system as that used with thefirst embodiment of the present invention shown in FIG. 3 can be used.That is, this servo pattern offers the advantage that it can be usedwith either of the two servo systems.

In the arrangement shown in FIG. 4, when the head travels on the track4n+2, the head reproduces the burst signals 8 and 9 simultaneously afterthe data in the data sector N has been read out. Assuming that the servosystem employed corresponds to the one used in the FIG. 3 arrangement,the frequency components f1 and f2 are discriminated in a discriminator,and if either of the two signals is found to exist, amplitude samplingsignals for the servo burst signals are generated. In this case, theservo burst signals M and N are detected in synchronism with theamplitude sampling signals, and the head position is controlled so thatthe amplitudes of the servo burst signals M and N are equal to eachother.

The embodiment in FIG. 4 can be modified in various ways. Though thearrangement is not shown, it is possible to position the group of burstsignals 8 and 9, or the group of servo burst signals K, L, M and N, onthe center lines of the tracks in FIG. 4. In such a case, both the priorart servo system discussed in conjunction with FIG. 1 and the firstembodiment of the present invention discussed in conjunction with FIG. 3could be used simultaneously. This arrangement would improve thelinearity of an error signal with respect to a track position that is tobe detected. For example, if the head travels at a position whichdeviates slightly from the center of the burst signal 8, but does notoverlap an adjacent track, the burst signal 9 would not be reproducedand the positioning error could not be reduced on the basis of signalshaving frequencies f1 and f2. However, even under these conditions, atleast two of the servo burst signals K, L, M and N can be detected,thereby permitting accurate detection of the amount of the positioningerror.

FIG. 5 shows a third embodiment of the present invention. In FIG. 5,reference numeral 10 denotes a data sector. Reference numeral 11 denotesa burst signal of frequency f1, and reference numeral 12 denotes a burstsignal of frequency f2. The burst signals 11 and 12 have the sameduration as the burst signals 8 and 9 in FIG. 4. Reference numerals 13and 14 denote burst signals 13 and 14 having a frequency of f1 and ashort duration. The burst signals 13 and 14 are separated in terms oftime. Reference numerals 15 and 16 denote burst signals having afrequency of f2. The burst signals 15 and 16 are also separated in termsof time.

The above-described arrangement will be discussed when the head travelson the track 4n+2. After the data has been read out from the sector N ofthe data sector 10, the head reproduces the burst signals 11 and 12simultaneously. The signals of the frequency components f1 and f2 arediscriminated by the discriminating circuit. The discriminating circuitis so arranged that if either of the signal exists, amplitude samplingsignals are generated. Amplitude sampling signals are generated threetimes, and at the first signal, the respective amplitudes of the signalsof the frequency component f1 and the frequency component f2 aremeasured simultaneously. Next, at the second signal, the mere existenceof the frequency component f1 or the frequency component f2 is detected.In this case, an f1 component signal and an f2 component signal havingthe same amplitude are measured (burst signals 11 and 12), and thensignals of the f2 component are detected twice (burst signals 15 and16).

Let us now suppose that an off track displacement of +1 track occurs. Atfirst, signals of the frequency components f1 and f2 having the sameamplitude are detected. Subsequently, a signal of the frequencycomponent f1 is detected (burst signal 13), and finally a signal of thefrequency component f2 is detected (burst signal 16), so that it can bedetermined that there is an off track displacement of +1 track.

Next, let us suppose that an off track displacement of +2 tracks occurs.At first, signals with frequency components f1 and f2 having the sameamplitude are measured. Subsequently, signals of the frequency componentf1 are detected twice consecutively. This is the same as the case inwhich there is an off track displacement of -2 tracks. Accordingly, itis not possible to determine the direction of the off trackdisplacement. Consequently, the servo capture range is ±2 tracks, whichis the same as in the embodiment shown in FIG. 2. However the period oftime of the servo signal can be shortened, and reliable operation isensured.

A fourth embodiment of the present invention is shown in FIG. 6. In FIG.6, the durations of burst signals 20, 21, 22 and 23, correspondingrespectively to the burst signals 13, 14, 15 and 16 shown in FIG. 5, areextended so that the durations are equal to those of burst signals 18and 19, corresponding respectively to the burst signals 11 and 12 inFIG. 5. In this arrangement, it is possible to measure the amplitude ofall the burst signals. Either the first group of burst signals, or agroup consisting of the second and the third burst signals, ispositioned on the track center lines. FIG. 6 shows an example where thesecond and the third burst signals are aligned with the track centerlines.

In the arrangement shown in FIG. 6, when the head travels along thetrack 4n+2, amplitude sampling signals are created in the same manner asin the embodiment shown in FIG. 5. At the first amplitude samplingsignal, the amplitudes of the burst signals 18 and 19 are measured, andmeasured values having the same amplitude are obtained for both. At thesecond amplitude sampling signal, the amplitude of the burst signal 22is measured to identify that this signal is a signal of the frequencyf2. At the third amplitude sampling signal, none of the burst signals ismeasured. That is, the detection of the frequency component f2 at thetime of the second amplitude sampling signal indicates that the head istravelling in the vicinity of the track 4n+2. Here, the amplitude ratioof the burst signals 18 and 19 measured due to the first amplitudesampling signal gives a position error.

When, for instance, an off track displacement of +1 track occurs, theamplitudes of the respective burst signals 18 and 19 are measured first.At the second amplitude sampling signal, none of the burst signals aremeasured, and then at the third amplitude sampling signal, the amplitudeof the burst signal 23 is measured to identify that this signal is asignal of the frequency f2. This makes it possible to determine that anoff track displacement of +1 track has occurred.

Next, when there is an off track displacement of +2 tracks, a signal ofthe frequency component f1 is detected due to the second amplitudesampling signal, and nothing is detected due to the third amplitudesampling signal. This is the same as the case in which there is an offtrack displacement of -2 tracks, so that the servo capture range is ±2tracks.

The advantage of this pattern is that it secures linearity of thepositioning error signal. For example, if there if an off trackdisplacement of approximately +0.5 track with respect to the track 4n+2,the first amplitude sampling signal only causes the burst signal 19 tobe sampled, and this sampling alone does not permit accurate calculationof the off track value. However, the amplitude of the burst signal 22 ismeasured due to the second amplitude sampling signal and the amplitudeof the burst signal 23 is measured due to the third amplitude samplingsignal, so that the value of the off track displacement can becalculated accurately by the amplitude ratio of the signals reproducedfrom burst signals 22 and 23.

As has been explained above, the servo pattern for controlling the headposition according to the present invention has a first pattern in whichtwo signals having different frequencies are arranged alternately in thewidth direction of a track in a two-track cycle, and a second patternwhich is repeated in a cycle of n tracks, and the first and the secondpatterns are arranged in the longitudinal direction of the tracks so asto create a servo pattern with a wide servo capture range and so as alsoto ensure accurate detection.

FIG. 7A repeats and extends the arrangement of the servo pattern shownin FIG. 3 for a magnetic disc, but the reference notations have beenaltered to facilitate the discussion presented below.

In FIG. 7A, reference numeral 31 denotes a data sector. Referencenumeral 32 denotes a pattern (hereinafter referred to as an f1 burst) onwhich a burst signal of the frequency f1 is recorded, and referencenumeral 33 denotes a pattern (hereinafter referred to as an f2 burst) onwhich a burst signal of the frequency f2 is recorded. A, B, C and D showpatterns (hereinafter referred to as servo bursts) on which burstsignals for servo control of the respectively corresponding frequenciesare recorded.

This arrangement of patterns will now be explained for the case in whicha magnetic head (not shown) travels along the track 4n+2. The head readsthe data recorded in the data sector N, and thereafter reproducessimultaneously the f1 burst 32 and the f2 burst 33. These frequencycomponents f1 and f2 are discriminated by a frequency discriminator (notshown), and when at least one of the frequency components exists, thereproduced amplitude levels of the servo bursts C and D are sample. Totrigger the samplings, amplitude sampling signals are generated, asshown in FIG. 7B. Further, as already explained above, if the samefrequency were used rather than different frequencies such as f1 and f2,the signals might cancel each other out due to phase shifts, resultingin unstable detection by the discriminating circuit. Since thesefrequencies f1 and f2 are selected to be different from the datarecording frequency (they are generally lower than the data recordingfrequency), there is no danger of erroneous detection in the data sector31.

The above-mentioned amplitude sampling signals are generated for a totalduration of four clock pulses, one signal at a time corresponding toeach of the servo bursts A, B, C, and D.

The reproduced signal level (amplitude) of each of the servo burst A, B,C, and D is measured in synchronism with each of the amplitude samplingsignals (1)-(4) corresponding to the servo bursts A, B, C and D,respectively. When the magnetic head is positioned on the track 4n+2,only the amplitudes of the servo bursts C and D are detected, and noamplitudes are detected for the servo bursts A and B. Then, headpositioning control is performed so that the amplitudes of the servobursts C and D are equal to each other. For example, when an off trackdisplacement of +1 track occurs (that is, when the head has beendisplaced one track inwards, so that the head is positioned on the track4n+3), the amplitudes of the servo bursts A and D become equal to eachother (see FIG. 7B), so that an off track of +1 track is judged.

Next, the situation in which an off track displacement of +2 tracksoccurs will be explained. In this case, the head is positioned on thetrack 4(n+1), so that the amplitudes of the servo bursts A and B becomeequal to each other. This condition, however, is the same as the case inwhich an off track displacement of -2 track occurs (that is, when thehead is positioned on the track 4n), so that it is not possible todetermine the head position. Consequently, the width of the servocontrol capture range is limited to less than ±2 tracks.

FIG. 8 shows another example of a servo pattern which performs the samefunction as that in FIG. 7A. This pattern is obtained by reversing theservo burst arrangement shown in FIG. 7A, and thus its explanation willbe omitted.

In FIG. 7B, the amplitudes of adjacent servo bursts are measured attracks 4n, 4n+1 and 4n+2. However at the position of track 4n+3, onlythe servo bursts A and D, at either end of the region which includes theservo bursts A, B, C, and D, are sampled.

As a result of this, the following problems arise at this trackposition.

(a) When a recording medium such as a flexible magnetic disc is used,the output level varies due to undesired factors such as variations infilm thickness or in magnetic characteristics. Consequently, when theamplitude of the reproduced servo burst signal is measured to performtracking control, a tracking error is likely to occur.

(b) Tracking control is performed according to the difference inamplitudes of the reproduced servo burst signals, so that there is thepossibility that the head is moved slightly by the actuator, even duringthe reading of the servo bursts. Consequently, if the distance betweenthe two reproduced servo bursts is large, it is not possible toaccurately measure the amplitudes, due to the variation of the headposition. This results in control errors.

Next, embodiments which solve these problems will be explained.

FIG. 9A shows a further embodiment of the present invention. In FIG. 9A,reference numeral 31 denotes a data sector. Reference numeral 32 denotesa pattern (the f1 burst) on which a burst signal of the frequency f1 isrecorded, and reference numeral 33 denotes a pattern (the f2 burst) onwhich a burst signal of the frequency f2 is recorded. A, B, C, D, and A'show patterns (the servo bursts) on which the burst signals of the samefrequency for servo control are recorded.

In this pattern arrangement, when the head travels along a track, the f1burst 32 and the f2 burst 33 are reproduced at the same time andamplitude sampling signals (see FIG. 9B) are generated, so that theamplitudes of the respective servo bursts A, A', B, C and D aremeasured. The amplitude sampling signals are generated for a totalduration of five pulses, one signal at a time, at the timing of therespective servo bursts.

FIG. 9B shows the measured burst amplitudes for the respective trackpositions. As shown in FIG. 9B, three servo bursts A, B and A' aremeasured for the track 4n, and three servo bursts A, D and A' are alsomeasured for the track 4n+3. Here, the two servo bursts A and B at thetrack 4n and the two servo bursts D and A' at the track 4n+3 aresufficient as the data for tracking control. With this arrangement, itis possible to compare the amplitudes of adjacent servo bursts at any ofthe tracks 4n, 4n+1, 4n+2 or 4n+3.

In this manner, with the servo burst arrangement shown in FIG. 9A, it ispossible to perform tracking control without using servo bursts attime-spaced positions even for the track 4n+3, thereby solving theproblems mentioned above. However, even with this servo patternarrangement, the width of the servo capture range is less than ±2tracks, and no problems occur.

In this embodiment of the present invention, there is one extra servoburst in the longitudinal direction of the track, i.e., in the directionof head movement, but the length of the servo burst portion is extremelyshort in comparison to the overall length of the track and thus this oneextra servo burst presents no problems.

FIG. 10 is an electrical block diagram showing one embodiment of anarrangement for reading the servo patterns shown in FIG. 9A to performtracking control. In FIG. 10, a reproduced signal A obtained from amagnetic head 100 is amplified by an amplifier 41, and then theamplified signal B is supplied to a data reproducing circuit 42 and toan automatic gain control (AGC) circuit 43. The output signal C from theAGC circuit 43 is inputted to amplifiers 44 and 45 and the respectivelyamplified signals E and F from the amplifiers 44 and 45 are supplied tof1 and f2 resonators 46 and 47, which detect the frequency components f1and f2.

The detection signals G and H from these resonators 46 and 47 are addedby an adder 48, and the added output I is detected by a detector 49.Then, the added output is converted into a digital signal by acomparator 50. In this manner, a servo pattern start signal K,indicating the starting time for reading the servo burst patterns, isoutputted from the comparator 50.

When the starting position of the servo burst patterns is detected asindicated by the signal K, a CPU 51 begins emitting amplitude samplingsignals L (see FIG. 9B), so that at the timing of the signal K the burstamplitudes are measured by a sample holder 52 and an A/D converter 53.That is, the sample holder 52 samples the signal C at the timing of thesignal K and outputs a sample hold signal M. The sample hold signal M issupplied to the A/D converter 53, which generates an 8-bit digital valueN, which is inputted to the CPU 51.

The CPU 51 performs the tracking control processing (explained in detailbelow) in accordance with an example of a control procedure shown inFIG. 11 to output a control signal U. This control signal U is convertedto an analog signal V by a D/A converter 54, and the signal V isamplified by a power amplifier 55 to provide a drive signal W to anactuator 56, so that the head 100 is driven.

FIG. 11 is a flowchart showing an example of arithmetic processing thatshould be executed by the CPU 51.

When the servo pattern start signal K is outputted from the comparator50, the CPU 51 is interrupted by the signal K, so that the servoprocessing routine shown in FIG. 11 is initiated.

Various symbols used in FIG. 11 are identified as follows.

SC: A counter indicating the number of samplings of the servo bursts.That is, the counter indicates the number of N sampling pulse of theamplitude sampling signals L, each sampling being performed at asampling pulse.

Mi: A memory for storage of A/D converted servo amplitude data. i=0, . .. , SC.

P: A 4-bit code indicating the type of the reproduced servo burst.

SP: A number (0, 1, 2 or 3) that indicates the servo pattern detected.

X: Burst data 1 for use in error calculation.

Y: Burst data 2 for use in error calculation.

Z: A burst error ratio indicating the order of any deviation in positionfrom the ideal center position of the track.

T: The lower 2 bits of the desired track position (track number).

ΔT: The number of error tracks between the current track and the desiredtrack.

Tp: Track pitch (length).

E: Error control amount (length).

An-1: Current actuator position.

An: Desired actuator position.

First, at step S2, the sampling counter SC is reset to "0".

At step S4, the amplitude sampling signal L (any of the pulses (1)-(5)shown in FIG. 9B) that corresponds to the value of the counter SC isoutputted.

At step S6, the burst amplitude data outputted from the A/D converter 53is written into the memory Mi at the corresponding SC address (i=0, . .. , SC).

At step S8, the content of the sampling counter SC is incremented by"1".

The above steps S4 through S8 are repeated until SC=5 is reached (stepS10). Through this procedure, the burst amplitude data corresponding topulses (1)-(5) of the amplitude sampling signals L shown in FIG. 9B arestored in the respective memories M0 through M4.

The stored values are then used to derive a code. If burst amplitudedata are stored in the memories M0 through M4, then (Mi)=1, and if noburst amplitude data are stored, then (Mi)=1, and if no burst amplitudedata are stored, then (Mi)=0, giving the code p=(M0)(M1)(M2)(M3)(M4)(step S12). For example, with respect to the track 4n shown in FIG. 9B,p=11001. For the track 4n+1, p=01100. For the track 4n+2, p=00110. Forthe track 4n+3, p=10011.

At steps S14, S18, S22 and S26, the value of the above-mentioned code pis determined, and then the burst amplitude data in relevant memories Miis stored in the register X and the register Y at steps S16, S20, S24and S28.

The burst error ratio Z is determined in accordance with the two burstamplitude data thus obtained at step S30. Here, the procedure does notsimply obtain the difference X-Y between the burst amplitudes, butrather obtains a burst error ratio given by Z=(X-Y)/(X+Y), whichindicates the degree of positional deviation of the head with respect tothe ideal center position of the track. When a magnetic disc is used asthe recording medium, the speed with respect to the head is greater atthe outer circumference than the inner circumference, so that the meredifference in burst amplitudes cannot produce a value indicating thedegree of the positional deviation of the head.

At step S32, the difference ΔT between the current track number(determined by steps S14, S18, S22 and S26) and the desired track numberis considered. If the magnetic head is positioned at the desired track,then ΔT becomes zero (ΔT=0).

At step S34, an error control amount E is obtained by adding the lengthobtained by multiplying the track pitch Tp by ΔT obtained above and thevalue (Tp/2)·Z. Here, (Tp/2) is a coefficient for converting the bursterror ratio Z into a length corresponding to the track pitch Tp.

At step S36, the error control amount E is added to the current positionAn+1 of the actuator 56 to obtain the desired actuator position An.

Finally, the above value An is inputted to the D/A converter 54, so thatthe actuator 56 is controlled at step S38.

An explanation of another embodiment follows.

FIG. 12 shows another embodiment of the present invention in whichpatterns are arranged in a reverse manner in comparison with that of theembodiment shown in FIG. 9A. With this pattern, the tracking control canalso be performed in the same manner as in the embodiment shown in FIG.9A.

Further, while both of the above embodiments use servo starting patternshaving two frequencies, it should be noted that an alternative startingpattern such as a bit pattern having a similar purpose (for example, thepulse trains A and B with different bit patterns discussed inconjunction with FIG. 2) can be used.

FIG. 13A shows a further embodiment of a servo pattern arrangementaccording to the present invention. In FIG. 13A, reference numeral 31denotes a data sector. Reference numeral 32 denotes a pattern (the f1burst) on which a burst signal of the frequency f1 is recorded, andreference numeral 33 denotes a pattern (the f2 burst) on which a burstsignal of the frequency f2 is recorded. A, B, C' and D' show patterns(the servo bursts) on which burst signals which are provided for servocontrol and which have the same frequency are recorded.

In this pattern arrangement, when the head travels along a track, the f1burst 32 and the f2 burst 33 are reproduced at the same time. Pulseswhich provide amplitude sampling signals (see FIG. 13B) are thengenerated, and the amplitudes of the respective servo bursts A, B, C'and D' are measured. The amplitude sampling signals are generated for atotal duration of four pulses, one signal at a time, at the timing ofthe respective servo bursts.

FIG. 13B shows the measured burst amplitudes for the respective trackpositions. As shown in FIG. 13B, two servo bursts are adjacent oneanother at the positions of the tracks 4n and 4n+2, and two servo burstsare time-spaced by one servo burst period at the positions of the tracks4n+1 and 4n+3.

In this manner, with the servo burst arrangement shown in FIG. 13A, itis possible to perform tracking control without using widely spacedservo bursts even for the track 4n+3, thereby solving the problemsdiscussed above in conjunction with FIG. 7B. Further, even with thisservo pattern arrangement, the width of the servo capture range is lessthan ±2 track, and no problems occur.

In order to read the servo pattern shown in FIG. 13A to perform trackingcontrol, the arrangement shown in FIG. 10 can be used. The arrangementis operated as explained already by using the processing shown in FIG.14.

FIG. 14 is a flowchart showing an example of the processing that shouldbe executed by the CPU 51.

When the servo pattern starting signal K is outputted from thecomparator 50, the CPU 51 is interrupted, and the servo processingroutine shown in FIG. 14 is initiated.

Various symbols used in FIG. 14 are identified as follows.

SC: A counter indicating the number of samplings of the servo bursts.That is, the counter indicates the number of a sampling pulse of theamplitude sampling signals L, each sampling being performed at asampling pulse.

Mi: A memory for storage of A/D converted servo amplitude data. i=0, . .. , SC.

P: A 4-bit code indicating the type of the reproduced servo burst.

SP: A number (0, 1, 2 or 3) that indicates the servo pattern detected.

X: Burst data 1 for use in error calculation.

Y: Burst data 2 for use in error calculation.

Z: A burst error ratio indicating the order of any deviation in positionfrom the ideal center position of the track.

T: The lower 2 bits of the desired track position (track number).

ΔT: The number of error tracks between the current track and the desiredtrack.

Tp: Track pitch (length).

E: Error control amount (length).

An-1: Current actuator position.

An: Desired actuator position.

First, at step S2, the sampling counter SC is reset to "0".

At step S4, the amplitude sampling signal L (any of the pulses (1)-(4)shown in FIG. 13B) that corresponds to the value of the counter SC isoutputted.

At step S6, the burst amplitude data outputted from the A/D converter 53is written into the memory Mi at the corresponding SC address (i=0, . .. , SC).

At step S8, the content of the sampling counter SC is incremented by"1".

The above step S4 through S8 are repeated until SC=4 is reached (stepS10). Through this procedure, the burst amplitude data (see FIG. 13B)corresponding to pulses (1)-(4) of the amplitude sampling signals Lshown in FIG. 13B are stored in the respective memories M0 through M3.

If burst amplitude data are stored in the memories M0 through M3, then(Mi)=1, and if no burst amplitude data are stored, then (Mi)=0, givingthe code p=(M0)(M1)(M2)(M3) (step S12). For example, with respect to thetrack 4n shown in FIG. 13B, p=1100. For the track 4n+1, p=0101. For thetrack 4n+2, p=0011. For the track 4n+3, p=1010.

At steps S14, S18, S22 and S26, the value of the above-mentioned code pis determined, and then the burst amplitude data in relevant memories Miis stored in the register X and the register Y at steps S16, S20, S24and S28.

The burst error ratio Z is determined in accordance with the two burstamplitude data thus obtained at step S30. Here, the procedure does notsimply obtain the difference X-Y between the burst amplitudes, butrather obtains a burst error ratio given by Z=(X-Y)/(X+Y), whichindicates the degree of positional deviation of the head with respect tothe ideal center position of the track. When a magnetic disc is used asthe recording medium, the speed with respect to the head is greater atthe outer circumference than the inner circumference, so that the meredifference in burst amplitudes cannot produce a value indicating thedegree of the positional deviation of the head.

At step S32, the difference ΔT between the current track number(determined by steps S14, S18, S22 and S26) and the desired track numberis considered. If the magnetic head is positioned at the desired track,then ΔT becomes zero (ΔT=0).

At step S34, an error control amount E is obtained by adding the lengthobtained by multiplying the track pitch Tp by ΔT obtained above and thevalue (Tp/2)·Z. Here, (Tp/2) is a coefficient for converting the bursterror ratio Z into a length corresponding to the track pitch Tp.

At step S36, the error control amount E is added to the current positionAn+1 of the actuator 56 to obtain the desired actuator position An.

Finally, the above value An is inputted to the D/A converter 54, so thatthe actuator 56 is controlled at step S38.

An explanation of another embodiment follows.

FIG. 15 shows a further embodiment of the present invention. In FIG. 15,A', B', C and D represent servo bursts having the same frequency. Inthis embodiment, the servo bursts A' and B' are positioned in reverse incomparison with those shown in FIG. 7A. Even with this pattern, trackingcontrol can be performed in the same manner as in the embodiment shownin FIG. 13A.

FIG. 16 shows another embodiment of the present invention. In thisembodiment, in place of the f1 burst 32 and the f2 burst 33, twopatterns X and Y having different bit patterns are used. For example,the pattern X may have 20 consecutive pulses, each having an interval1T, and thereafter 5 consecutive pulses, each having an interval 2T. Thepattern Y may have 10 consecutive pulses, each having an interval 1T,and thereafter 10 consecutive pulses, each having an interval 2T.

These patterns X and Y are used as a read starting mark for sampling theservo bursts A, B, C and D. Furthermore, as shown by the broken lines inFIG. 16, it is possible, like in the embodiments shown in FIG. 13A andin FIG. 15, to change the positions A and B to the positions A' and B',and the positions C and D to the positions C' and D', respectively.

Further, if the layout of the servo bursts is varied in the embodimentsalready explained, track positions occur at which the tracking controlis performed in the opposite direction. It is possible to accommodatethis case by changing the control algorithm according to the modifiedservo burst layout.

FIG. 17A shows a further embodiment of a servo pattern according to thepresent invention. In FIG. 17A, reference numeral 31 denotes a datasector. Reference numeral 32 denotes a pattern (the f1 burst) on which aburst signal of the frequency f1 is recorded, and reference numeral 33denotes a pattern (the f2 burst) on which a burst signal of thefrequency f2 is recorded. A, A', B, C and D show patterns (the servobursts) on which the burst signals which are provided for servo controland which have the same frequency are recorded.

In this pattern arrangement, when the head travels along a track, the f1burst 32 and the f2 burst 33 are reproduced at the same time. Amplitudesampling signals (see FIG. 17B) are then generated, and the amplitudesof the respective servo bursts A, A', B, C and D are measured. Theamplitude sampling signals are generated for a total duration of fourpulses, one signal at a time, at the timing of the respective servobursts.

FIG. 17B shows the measured burst amplitudes for the respective trackpositions. As shown in FIG. 17B, at the positions of the track 4n andtrack 4n+3, a third burst indicated by (A) or (A') is measured, but onlyan adjacent pair of bursts is needed to perform tracking control. At anyof the tracks 4n, 4n+1, 4n+2 and 4n+3, it is possible to compareadjacent servo burst amplitudes.

In this manner, with the servo burst arrangement shown in FIG. 17A, itis possible to perform tracking control without using servo bursts attime-spaced positions even for the track 4n+3, thereby solving theproblems discussed in conjunction with FIG. 7B. Further, even with thisservo pattern arrangement, the width of the servo capture range is lessthan ±2 track, and no problems occur.

In order to read the servo pattern shown in FIG. 17A to perform trackingcontrol, the arrangement shown in FIG. 10 can be used. The arrangementcan be operated by executing in CPV 51 the program shown in FIG. 18.

When the servo pattern starting signal K is outputted from thecomparator 50, the CPU 51 is interrupted, and the servo processingroutine shown in FIG. 18 is initiated.

Various symbols used in FIG. 18 are identified as follows.

SC: A counter indicating the number of samplings of the servo bursts.That is, the counter indicates the number of a sampling pulse of theamplitude sampling signals L, each sampling being performed at asampling pulse.

Mi: A memory for storage of A/D converted servo amplitude data. i=0, . .. , SC.

P: A 4-bit code indicating the type of the reproduced servo burst.

SP: A number (0, 1, 2 or 3) that indicates the servo pattern detected.

X: Burst data 1 for use in error calculation.

Y: Burst data 2 for use in error calculation.

Z: A burst error ratio indicating the order of any deviation in positionfrom the ideal center position of the track.

T: The lower 2 bits of the desired track position (track number).

ΔT: The number of error tracks between the current track and the desiredtrack.

Tp: Track pitch (length).

E: Error control amount (length).

An-1: Current actuator position.

An: Desired actuator position.

First, at step S2, the sampling counter SC is reset to "0".

At step S4, the amplitude sampling signal L (any of the pulses (1)-(4)shown in FIG. 17B) that corresponds to the value of the counter SC isoutputted.

At step S6, the burst amplitude data outputted from the A/D converter 53is written into the memory Mi of the corresponding SC address (i=0, . .. , SC).

At step S8, the content of the sampling counter SC is incremented by"1".

The above steps S4 through S8 are repeated until SC=4 is reached (stepS10). Through this procedure, the burst amplitude data (see FIG. 17B)corresponding to pulses (1)-(4) of the amplitude sampling signals Lshown in FIG. 17B are stored in the respective memories M0 through M3.

If burst amplitude data are stored in the memories M0 through M3, then(Mi)=1, and if no burst amplitude data are stored, then (Mi)=0, givingthe code p=(M0)(M1)(M2)(M3) (step S12). For example, with respect to thetrack 4n shown in FIG. 17B, p=1110. For the track 4n+1, p=0110. For thetrack 4n+2, p=0011. For the track 4n+3, p=1011.

At steps S14, S18, S22 and S26, the value of the above-mentioned code pis determined, and then the burst amplitude data in relevant memories Miis stored in the register X and the register Y at steps S16, S20, S24and S28.

The burst error ratio Z is determined in accordance with the two burstamplitude data thus obtained at step S30. Here, the procedure does notsimply obtain the difference X-Y between the burst amplitudes, butrather obtains a burst error ratio given by Z=(X-Y)/(X+Y), whichindicates the degree of positional deviation of the head with respect tothe ideal center position of the track. When a magnetic disc is used asthe recording medium, the speed with respect to the head is greater atthe outer circumference than the inner circumference, so that the meredifference in burst amplitudes cannot produce a value indicating thedegree of the positional deviation of the head.

At step S32, the difference ΔT between the current track number(determined by steps S14, S18, S22 and S26) and the desired track numberis considered. If the magnetic head is positioned at the desired track,then ΔT becomes zero (ΔT=0).

At step S34, an error control amount E is obtained by adding the lengthobtained by multiplying the track pitch Tp by ΔT obtained above and thevalue of (Tp/2)·Z. Here, (Tp/2) is a coefficient for converting theburst error ratio Z into a length corresponding to the track pitch Tp.

At step S36, the error control amount E is added to the current positionAn+1 of actuator 56 to obtain the desired actuator position An.

Finally, the above value An is inputted to the D/A converter 54, so thatthe actuator 56 is controlled at step S38.

An explanation of another embodiment follows.

FIG. 19 shows another embodiment of the present invention. In thisarrangement, the servo burst D' replaces the servo burst A' shown in theembodiment in FIG. 17A. This pattern permits the same tracking controlas in the embodiment shown in FIG. 17A.

FIG. 20 shows a further embodiment of the present invention, in which aservo burst E' is positioned by two burst intervals ahead of the servoburst E.

FIG. 21 shows a still further embodiment of the present invention, inwhich a servo burst H' is positioned two burst intervals behind theservo burst H.

As a yet further embodiment of the present invention, it is possible touse both the servo burst A' of the embodiment shown in FIG. 17A and theservo burst D' of the embodiment shown in FIG. 19. In a like manner, itis possible to use both the servo burst E' and the servo burst H' of theembodiments shown in FIG. 20 and FIG. 21.

FIG. 22 shows a further embodiment of the present invention. In thisembodiment, in place of the f1 burst 32 and the f2 burst 33, twopatterns X and Y having different bit patterns are employed. Forexample, the pattern X may have 20 consecutive pulses, each having aninterval 1T, and thereafter 5 consecutive pulses, each having aninterval 2T. The pattern Y may have 10 consecutive pulses, each havingan interval 1T, and thereafter 10 consecutive pulses, each having aninterval 2T.

These patterns X and Y are used as a read starting mark for sampling theservo bursts A, B, C and D.

Furthermore, as shown by broken line boxes in FIG. 22, it is possible touse at least one of A' and D' like in the embodiments shown in FIG. 17Aand in FIG. 19.

As has been explained above, the present invention makes it possible todetect continuously burst amplitude data for use in servo control, sothat stable tracking control is ensured with less control error.

What is claimed is:
 1. A storage device comprising:a) a plurality ofdata storing sectors for storing data in accordance with a predeterminedformat which defines a plurality of tracks divided into said pluralityof sectors, said plurality of data storing sectors being serially formedin a first direction at a predetermined interval; and b) a plurality ofposition control signal storing portions each formed between said datastoring sectors to indicate positions of said data storing sectors,saidposition control signal storing portions each including:a first storingportion which stores a first position control signal including a firstfrequency signal component, a second storing portion which stores asecond position control signal including a second frequency signalcomponent different from said first frequency signal component, and athird position storing portion which stores a plurality of thirdposition control signals, said first storing portion and said secondstoring portion being adjacently formed in a second directionperpendicular to said first direction, said third position controlsignals being formed adjacently to said first storing portion and saidsecond portion in the first direction, and said third position controlsignals being sequentially shifted in said first direction and saidsecond direction for each track of a set of tracks associated with saidthird portion control signals; said first position control signal andsaid second position control signal being used for timing control ofreading said third position control signals, and said third positioncontrol signals are used for positional control of reading said datastored in said data storing sectors.
 2. A storage device as claimed inclaim 1, wherein said third position control signals include a frequencycomponent different from said first and second frequency signalcomponents.
 3. A storage device as claimed in claim 1, wherein saidfirst storing portion and said second storing portion are formed spacedapart from said data storing portions by a predetermined pitch in saidsecond direction.
 4. A storage device as claimed in claim 1, whereinsaid first and second storing portions are so arranged that each extendsover two adjacent tracks.
 5. A storage device as claimed in claim 4,wherein said first and second storing portions have lengths in saidfirst direction which are different from the length of said thirdposition storing portions in said first direction.
 6. A storage deviceas claimed in claim 4, wherein said first and second storing portionsare displaced by half a track pitch from said tracks in a widthdirection of said tracks.
 7. A disc-shaped storage device comprising:a)a plurality of data storing sectors for storing data in accordance witha predetermined format which defines a plurality of concentric tracksdivided into said plurality of sectors, said plurality of data storingsectors being serially formed in a first direction at a predeterminedinterval; and b) a plurality of position control signal storage portionseach of which is formed between said data storing sectors to indicatepositions of said data storing sectors;said position control signalstoring portions, each including:a first storing portion which stores afirst position control signal including a first frequency signalcomponent; a second storing portion which stores a second positioncontrol signal including a second frequency signal component differentfrom said first frequency signal component; and a third storing portionwhich stores a plurality of third position control signals including athird frequency signal component different from said first and secondfrequency signals; wherein said first storing portion and said secondstoring portion are adjacently formed in a second directionperpendicular to said first direction; said third position controlsignals are formed adjacently to said first storing portion and saidsecond portion in said first direction along said tracks; said thirdposition control signals are sequentially shifted in said firstdirection and said second direction for each track of a set of tracksassociated with said third portion control signals; said first positioncontrol signal and said second position control signal are used fortiming control of reading said third position control signals; and saidthird position control signals are used for positional control ofreading said data stored in said data storing sectors.
 8. A disc-shapedstorage device as claimed in claim 7 wherein said first and secondstoring portions are so arranged that each extends over two adjacenttracks.
 9. A disc-shaped storage device as claimed in claim 8, whereinsaid first and second storing portions are displaced by half a trackpitch from said tracks in a width direction of said tracks.
 10. Adisc-shaped storage device as claimed in claim 7, wherein said first andsecond storing portions have lengths in said first direction which aredifferent from the length of said third storing portions in said firstdirection.
 11. A disc-shaped storage device as claimed in claim 7,wherein said device is a magnetic recording/reproducing disc.